Science Experiments

“Book of How” Excerpt: How to Make A Rainbow

By: Highlights Editorial
Book of How cover next to image of a rainbow.
Ages 3+
Critical Thinking
Fine Motor Skills

Have you ever wondered how rainbows form? The Highlights Book of How helps you answer your kids the next time they ask what makes a rainbow!

If rainbows seem magical, it’s because they sort of are!  

Rainbows are optical illusions—a type of image that tricks our brains—formed by moisture and light.

After it rains, or when water sprays from a fountain or hose, lots of water hangs in the air. If sunlight hits these droplets of water at just the right angle, the light scatters. This only happens when the sun is in the opposite end of the sky from the droplets—so if you are looking at a rainbow, the sun will always be behind you.  

Sunlight does not normally appear as color because it is white. But white light is actually made up of all colors. When the sunlight scatters, it is split up into its separate colors. To us, this looks like a rainbow. However, rainbows don’t actually exist in one place. Because a rainbow is made of light, its appearance and position can vary slightly depending on where a person is standing. Plus, rainbows are actually circles! Humans can only see half of this circle, as the other half is below the horizon. After the raindrops fall from the air or the sun moves its position, the rainbow will disappear—just like magic.

If rainbows seem magical, it’s because they sort of are!

How to Make a Rainbow

Make a little colorful rainbow magic with this simple experiment!

What You’ll Need:

  • White paper 
  • A sunny windowsill 
  • Small clear glass 
  • Water  

What You’ll Do:

1. Put the paper down on the windowsill or other flat spot in bright sun. 

2. Fill the glass a little over halfway with water 

3. If you don’t see a rainbow, carefully pick up the glass and lift it slowly straight up.

How It Works:

The sunlight we see has all the colors mixed together in it. When light moves through water, it refracts, or bends. Each drop of water acts like a tiny prism, splitting the light into all the colors of the rainbow. 

Extend the Fun:

Make a rainbow using a garden hose. Just squeeze the hose handle gently so that the water comes out in a fine mist. Stand with the sun behind you and point the water in different directions until your rainbow is bright and colorful.

Still have questions about what happens in the sky above us? Head here to find out why the sky is blue!

Did you love this excerpt from page 182 of The Highlights Book of How? With 352 pages of experiments, activities and answers to kids’ questions, The Highlights Book of How is a perfect gift for inquisitive kids.

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By: Highlights Editorial